In an exposure apparatus used in manufacture of devices such as semiconductor devices, light emitted from a light source travels through a fly's eye lens as optical integrator to form a secondary light source (which is generally a predetermined light intensity distribution on an illumination pupil) as a substantial surface illuminant consisting of a large number of light sources. The light intensity distribution on the illumination pupil will be referred to hereinafter as “pupil intensity distribution.” Furthermore, the illumination pupil is defined as a position such that by action of an optical system between the illumination pupil and an illumination target surface (a mask or a wafer in the case of the exposure apparatus), the illumination target surface is kept as a Fourier transform surface of the illumination pupil.
Light from the secondary light source is condensed by a condenser optical system and thereafter illuminates the mask with a predetermined pattern formed thereon, in a superimposed manner. Light transmitted by the mask travels through a projection optical system to be imaged on the wafer, whereby the mask pattern is projected (or transferred) onto the wafer. Since the pattern formed on the mask is micronized, it is indispensable to obtain a homogeneous illuminance distribution on the wafer, in order to implement accurate transfer of the microscopic patter onto the wafer.
There is the conventionally-proposed illumination optical system capable of continuously changing the pupil intensity distribution (and, in turn, an illumination condition) without use of a zoom optical system (e.g., cf. Patent Literature 1). This illumination optical system uses a movable multi-mirror composed of a large number of microscopic mirror elements which are arranged in an array pattern and inclination angles and inclination directions of which are individually driven and controlled, to divide an incident beam into microscopic units corresponding to respective reflective faces and deflect divided beams, thereby to convert a cross section of the beam into a desired shape or a desired size and, in turn, to realize a desired pupil intensity distribution.